Why elliptical orbits and not circular

But they are actually ellipses, and this was first worked out in the early s by Johannes Kepler. That honor is held by Aristarchus of Samos, a Greek philosopher who lived in the second century B. Given the lack of proper instrumentation, the debate over whether the Earth or Sun was the center of the universe continued over many centuries. In , Polish astronomer Nicolaus Copernicus published a mathematical treatise that promoted the idea of the Sun being the center of the solar system.

But his treatment was complicated, and it was Kepler who used data to come up with the realization that the orbit of planets were ellipses. In fact, Kepler came up with three laws. They are: 1 the orbit of a planet is an ellipse, with the Sun at one of the two foci; 2 the line connecting the planet and Sun sweeps out equal areas during equal intervals of time and; 3 the square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.

The semi-major axis is the distance from the center of the ellipse to the edge along the longest distance. In a mathematical sense, the third law is the most interesting, as it allows astronomers to relate how long it takes for a planet to go once around the Sun to its distance from the Sun. For instance, the closest the Earth gets to the Sun is 91 million miles or about million kilometers.

When the Earth is at aphelion, it is nearly 95 million miles or about million kilometers from the Sun. It also means that the foci are actually not that far apart, only about 4 million miles.

To give some perspective, the radius of the Sun is about , miles and the distance between the Sun and Mercury is 29 million miles perihelion. Because the distance between the planet and Sun is smaller at perihelion than at aphelion, it must mean that the planet moves faster at perihelion. For the Earth, the difference is 30 kilometers per second at perihelion and 29 kilometers per second at aphelion, or a little over half a mile per second difference. Learn more about the misconceptions of science.

He just used some precise observations and figured out what happened. Taking this equation and others he had derived, Newton could calculate that the orbit of planets should be elliptical. Are there telescopes that can see the flag and lunar rover on the Moon?

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Beginner How do you measure the distance between Earth and the Sun? Intermediate Can artificial gravity be created in space? Intermediate At what speed does the Earth move around the Sun? Beginner How does the position of Moonrise and Moonset change? Intermediate Why do we not have eclipses every month? How long could life on Earth survive if the Sun stopped shining? Beginner Are there telescopes that can see the flag and lunar rover on the Moon? Beginner Can artificial gravity be created in space?

Intermediate How does the position of Moonrise and Moonset change? Beginner How can we see the Milky Way if we are inside it? Intermediate But seriously: what was there before the Big Bang? Intermediate Are there telescopes that can see the flag and lunar rover on the Moon?

Beginner Is the Moon moving away from the Earth? When was this discovered? Intermediate Why is the moon in a different place every night? What's going to happen on December 21st ? Intermediate What color is each planet? Stage and screen. Birds and the bees. Why not circular? Donald Fleming, London, UK Orbits are eliptical because of Newtons Law of Gravity bodies attract each other in proportion to their mass and inversly proportional to the square of the distance between them.

All worked out by Kepler some years ago. A circular orbit is a special and very unlikely case of an eliptical orbit. Bob Kirk, Bangkok, Thailand Yes. Isaac Newton. Read his Principia Mathematica. Peter Brooke, By Kinmuck, Scotland, UK It's not easy to arrange a perfectly circular orbit for an inverse-square law - just a small tweak either in the initial conditions, or from interplanetary interactions or impacts will change the path from a circular orbit to an elliptical one.

But, if you look at an ellipse from the right angle, it will appear circular. So, consider it a matter of viewpoint! Michael Hall, Canberra, Australia The shape of planetary orbits follows from the observed fact that the force of gravity between two objects depends on the square of the distance between them.

If you double the distance between two objects, the attractive force between them drops to a quarter of it's original value. If you triple the distance it drops to a ninth. Isaac Newton demonstrated mathematically that this law implied that the path followed by an object in a gravity field would be a parabola, a hyperbola or an ellipse.

The first two are open ended. If something entered the solar system on a parabolic or hyperbolic path, we would see it just once before it disappeared into the distance.